This invention relates in general to internal drum scanner assemblies and laser imaging systems incorporating such scanner assemblies. In particular, the present invention relates to a mechanism for aligning film into a scanning position in an internal drum type scanner assembly, suitable for use in a medical imaging system.
Laser imaging systems are commonly used to produce photographic images from digital image data generated by magnetic resonance (MR), computed tomography (CT) or other types of medical image scanners. Systems of this type typically include a continuous tone laser imager for exposing the image on photosensitive film, a film processor for developing the film, and control subsystems for coordinating the operation of the laser imager and the film processor.
The digital image data is a sequence of digital image values representative of the scanned image. Image processing electronics within the control subsystem processes the image data values to generate a sequence of digital laser drive values (i.e., exposure values), which are input to a laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film in a raster pattern for exposing the image on the film.
The continuous-tone images used in the medical imaging field have very stringent image-quality requirements. A laser imager printing onto transparency film exposes an image in a raster format, the line spacing of which must be controlled to better than one micrometer. In addition, the image must be uniformly exposed such that the observer cannot notice any artifacts. In the case of medical imaging, the observers are professional image analysts (e.g., radiologists).
Film exposure systems are used to provide exposure of the image on photosensitive film. Known film exposure systems include a linear translation system and a laser or optical scanning system. The laser scanning system includes a laser scanner with unique optical configurations (i.e., lenses and mirrors) for exposure of the image onto the film. The linear translation system provides for movement of the laser scanning system in a direction perpendicular to the scanning direction, such that a full image may be scanned on a piece of photosensitive film.
In an internal drum type laser scanner assembly, a piece of film is positioned onto a film platen, wherein the film platen has a partial cylindrical or partial drum shape. The photosensitive film is positioned against the film platen. The laser or optical scanning system is positioned at the center of curvature of the photosensitive film for scanning a scan line across the photosensitive film surface. A linear translation system moves the laser or optical scanning system lengthwise along a longitudinal axis as defined by the center of curvature of the film to expose an entire image onto the film.
The film may be fed onto the film platen utilizing a film transport system which often incorporates a plurality of feed rollers. Once the piece of photosensitive film is fed onto the film platen, the film must be held tight against the curved surface of the film platen, and centered and aligned into a scanning position in order for an image to be correctly exposed onto the photosensitive film. Any skew of the film must also be removed. Often such methods and mechanisms for aligning and centering a piece of film on the internal surface of the film platen require multiple complex mechanical and electrical components and control systems.
U.S. Pat. No. 5,956,071, issued Sep. 21, 1999, inventors Mattila et al., discloses an assembly for positioning a film into a scanning position on a curved film platen in an internal drum scanner assembly. The film platen is defined by a first curved edge, a second curved edge, a film feed edge, and a film stop edge. The assembly comprises a first slider block assembly and a second slider block assembly which is spaced from the first slider block assembly a distance less than the width of the leading edge of the photosensitive film. A feed mechanism is positioned proximate the film feed edge, for feeding a piece of photosensitive film having a leading edge along the curved film platen. The leading edge of the film is fed from a location proximate the film feed edge towards the film stop edge. When the photosensitive film is in the scanning position, the leading edge of the photosensitive film contacts the first slider assembly and the second slider assembly. The photosensitive film is tensioned against the curved film platen in alignment between the first slider assembly and the second slider assembly and the feed mechanism, thus removing any skew.
As disclosed in the previous patent, different film sizes are accommodated by a set of a first and second slider block assemblies being provided for each film size handled by the scanner assembly. The slider block assembly sets are spaced along the curved length of the platen since different film lengths wrap around the platen to varying degrees. Although useful for the purposes for which it was intended, this arrangement adds undesirable complexity in that it requires changing slider block assembly locations for each film size.
There is thus a need in an internal drum type laser scanner assembly to provide a system for properly registering multiple film sizes within the drum that is reliable, low in cost and simple in design.
According to the present invention, there is provided a solution to the problems and need discussed above.
An apparatus for registering film in a drum scanner assembly comprising;
a concave curved film platen having spaced first and second linear edges that are oriented horizontally and third and fourth curved side edges connected between said first and second edges, said concave, curved film platen having a curved surface defining a curved film path having a first downwardly curved position and a second upwardly curved position from said first to said second edges, first and second spaced film engagement assemblies independently and movably mounted relative to said platen at said second portion of said film path, said assemblies having film registration slides for engaging the leading edge of a sheet of film fed onto said concave, curved film platen from said first edge and along said curved film path said slides being mounted for movement over substantially the length of said second portion of said path and being adapted to register films of different lengths; and
means associated with said slides for biasing said slides through the force of gravity against said leading edge of said film, wherein as said film is fed along said curved path, said slides are moved upwardly by said film against the force of gravity wherein said film is caused to conform to the curved film platen and wherein said independently mounted slides act to remove skew from said fed film.
The invention has the following advantages.
1. Handles multiple film sizes.
2. Precise control of motion of film registration mechanism.
3. Reliability.
4. Ease of assembly.